1. I've disabled the use of indevidual error sites but still I can see and change them in the error directory. 2. For an other user a have disabled the error sites but I don't now how to activate them.
That are ISPconfig's standard error pages, not customized ones. There's a checkbox on the "Basis" tab of a web site where you can enable individual error pages.
But the user can change them. Where is the different between this and the customized ones? I know but in that case the checkbox is gone and I don't know wherever it is...
If the user has enough knowledge, then yes. We might have to change the permissions... Please check if you enabled individual error pages for the reseller in ISPConfig.